Patent GB-889494-A (GB)
Title: Improvements in or relating to agricultural implement depth control
IPC: A01B63/114
Filed: 1960-08-19
Abstract: 889,494. Tractor power lift mechanisms. PORSCHE - DIESEL - MOTORENBAU G.m.b.H. Aug. 19, 1960 [Sept. 5, 1959], No. 28768/60. Class 79(1). An automatic depth control arrangement for implements connected by a quadrilateral guide linkage to a tractor comprises hydraulic raising and lowering means, sensing means connected therewith to selectively raise or lower the implement, the lower links of the guide linkage being pivoted to the tractor, and the sensing means being connected to the tractor coaxially with the pivot axis of the lower links. The quadrilateral guide linkage having pivot points a, b, c, d, comprises a pair of lower links 4, 4<SP>1</SP>, and an upper link 7 to which the implement 5 is attached by a head piece 6. The lower links are connected by struts 9, 9<SP>1</SP> to the power lift arms 10, 10<SP>1</SP> which are operated by a piston 12 and cylinder 13 under the control of a valve 15. The power unit comprises a supply line 16, 20, return line 18, 22, pump and reservoir 23. The valve 15 may be controlled by a handle 19 which may be put in positions N, H, S corresponding to "neutral", "lift" and "lower". A pressure line 29, 29<SP>1</SP> is connected between the cylinder 13 and reservoir 23 and includes a manually operable throttle valve 31 and a throttle valve 28 attached to one arm 27 of a sensing member 24 which comprises arms 27, 27<SP>1</SP> pivoted coaxially at 3 with the lower lift arms and a cross-member 25. The valve 28 comprises a rotary member 32, Fig. 5, operated by a member 34 connected to a drag lever 36 also pivoted at 3 and connected by a bifurcated member 37 to the lower link 4. A sensing arm 26 is clamped to the arm 25 by a laterally adjustable clamp 40 adjustable also relative to the member 25 by a spindle 42 and is downwardly urged against a stop 45 by a spring 44 (Fig. 11). The working depth of the implement is set by adjusting the length of link 7, and at the commencement of an operation, the valve 15 is set to lift and the valve 31 is opened so that a limited pressure is generated in the cylinder 13 determined by the initial setting of valve 28. The arm 26 is adjusted to touch the ground surface and is raised if the ground level rises, thereby causing relative movement between the arms 26 and 27 and by virtue of member 34 operation of valve 28 (throttling) to increase the pressure in line 29 and operation of piston 12 with the consequent raising of the lift arms to maintain a constant working depth of the implement. If the ground surface falls away and the arm 26 descends, the valve 28 is moved to an open position allowing the implement to descend freely. The implement may be lifted (at the end of a furrow) by manually closing valve 31. When the arms 4, 4<SP>1</SP> are lifted, the sensing member 24 is also lifted by an abutment 38, Fig. 3. The weight on the back wheels 48 of the tractor may be increased (weight transfer) by partially closing the valve 31 to a throttling position whereby a pressure is created in the cylinder 13 below the pressure required to lift the implement. Sudden shocks, as might occur if a large stone is encountered, are prevented by rotation of member 26 relatively to member 24 against the pressure of spring 44. In a modification, Fig. 8, the sensing device 24<SP>1</SP> is connected by a flexible cable 55 to the control valve of the cylinder 13. The flexible cable is connected to an abutment member 38<SP>1</SP> and to the operating handle 19<SP>1</SP> of the valve, the sleeve of the cable being connected to a stop 50 and to a member 51 of the sensing device 24<SP>1</SP>. When the sensing device moves upwardly (due to change in ground elevation), the relative movement between the cable and sleeve being as if the arms 4<SP>11</SP> moved downwardly, and the handle 19<SP>1</SP> is moved to the "lifting" position. In the reverse sequence, the handle 19<SP>1</SP> is pushed to the "lower" position when the device 26<SP>1</SP> enters a depression. The sensing skid 26 may be equipped with a wheel.